Rapid, simple, and sensitive immunoagglutination assay with SiO2 particles and quartz crystal microbalance for quantifying Schistosoma japonicum antibodies

Abstract

Background: The resurgence of the parasitic disease schistosomiasis calls for more efficient diagnostic tests. We developed a rapid, simple, portable, and sensitive immunoagglutination assay that uses SiO2 particles and quartz crystal microbalance (QCM) for quantifying Schistosoma japonicum (Sj) antibodies (SjAb). Methods: We prepared submicrometer-sized silica particles derivatized with Sj antigens as replacements for traditional latex microspheres to specifically agglutinate in the presence of SjAb targets, and we used the QCM monitor to measure the resulting frequency shifts. We optimized the assay medium by adding poly(ethylene glycol) (PEG) as a response accelerator of immunoagglutination. To minimize or eliminate any nonspecific agglutination or adsorption interferences, we conducted appropriate sealing procedures separately for silica particles and the QCM probe. Results: The measured frequency changes were linearly related to the SjAb concentrations in infected rabbit serum. The PEG-assisted immunoagglutination system was quantitatively sensitive to SjAb concentrations ranging from ∼0.70 to 32.31 mg/L, with a detection limit of ∼0.46 mg/L. The obtained linear regression equation was: y = 43.61 x + 80.44 (r = 0.9872). Several serum specimens were evaluated with the developed QCM immunoassay and the results were compared with ELISA, validating the feasibility of practical applications. Conclusions: This novel immunoagglutination-based QCM detection format is rapid, simple to use, and more portable than conventional diagnostic immunoassays, thus offering a promising alternative tool that can be used for point-of-care clinical diagnosis of schistosomiasis, particularly in epidemic situations. © 2006 American Association for Clinical Chemistry.